The ion plasma electron gun of the present invention is of the same general type as the gun disclosed in U.S. Pat. No. 3,970,892. As stated in that patent, a recent advance in the art of generating high energy electron beams for use, for example, in e-beam excited gas lasers, is the plasma cathode electron gun. In such an electron gun a plasma is produced in a hollow cathode discharge between the hollow cathode surface and an anode grid operated at relatively low voltage with respect to the cathode. Electrons are extracted from the discharge plasma through the anode grid and a control grid, and these electrons are accelerated to high energies in a plasma-free region between the grids and an accelerating anode which, typically, is a thin foil window maintained at a relatively high voltage with respect to the cathode. Among the advantages of the plasma cathode electron gun are its structural simplicity and ruggedness, high controlability and efficiency, low cost, and suitability for producing large area electron beams.
A second Patent, namely U.S. Pat. No. 4,025,818 discloses an ion plasma electron gun which is essentially similar to the gun disclosed in U.S. Pat. No. 3,970,892, with the addition of a wire anode for the plasma discharge and a number of baffles which allow the plasma chambers to be connected sequentially.
The electron distribution of the electron beams generated by the tubes of U.S. Pat. Nos. 3,970,892 and 4,025,818 are generally peaked in the center and gradually diminish to zero at the edges of the foil window. An important objective of the present invention is to provide an improved structure which generates an electron beam with uniform electron distribution across the entire beam as it emerges from the foil window.
Another object of the invention is to provide such an improved ion plasma electron gun which is constructed for long run time operation and for high efficiency.